Global warming only decrease the extent off the ice in polar regions, right. Well maybe not so. The first direct evidence that marked changes to Antarctic sea ice drift have occurred over the last 20 years, in response to changing winds, is published this week in the journal Nature Geoscience. Scientists from NERC’s British Antarctic Survey (BAS) and NASA’s Jet Propulsion Laboratory (JPL), Pasadena California explain why, unlike the dramatic losses reported in the Arctic, the Antarctic sea ice cover has increased under the effects of climate change.

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The Antarctic ice sheet is one of the two polar ice caps of the Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth. It covers an area of almost 14 million square km and contains 30 million cubic km of ice. That is, approximately 61 percent of all fresh water on the Earth is held in the Antarctic ice sheet, an amount equivalent to 70 m of water in the world's oceans. In East Antarctica, the ice sheet rests on a major land mass, but in West Antarctica the bed can extend to more than 2,500 m below sea level. The land in this area would be seabed if the ice sheet were not there.

Maps created by JPL using over 5 million individual daily ice motion measurements captured over a period of 19 years by four US Defense Meteorological satellites show, for the first time, the long-term changes in sea ice drift around Antarctica.

"Until now these changes in ice drift were only speculated upon, using computer models of Antarctic winds. This study of direct satellite observations shows the complexity of climate change. The total Antarctic sea-ice cover is increasing slowly, but individual regions are actually experiencing much larger gains and losses that are almost offsetting each other overall. We now know that these regional changes are caused by changes in the winds, which in turn affect the ice cover through changes in both ice drift and air temperature. The changes in ice drift also suggest large changes in the ocean surrounding Antarctica, which is very sensitive to the cold and salty water produced by sea-ice growth."

"Sea ice is constantly on the move; around Antarctica the ice is blown away from the continent by strong northward winds. Since 1992 this ice drift has changed. In some areas the export of ice away from Antarctica has doubled, while in others it has decreased significantly." says lead author, Dr Paul Holland of BAS.

he new research also helps explain why observed changes in the amount of sea-ice cover are so different in the two Polar Regions. The Arctic has experienced dramatic ice losses in recent decades while the overall ice extent in the Antarctic has increased slightly. However, this small Antarctic increase is actually the result of much larger regional increases and decreases, which are now shown to be caused by wind-driven changes. In places, increased northward winds have caused the sea-ice cover to expand outwards from Antarctica. The Arctic Ocean is surrounded by land, so changed winds cannot cause Arctic ice to expand in the same way.

Dr Ron Kwok, JPL says,

"The Antarctic sea ice cover interacts with the global climate system very differently than that of the Arctic, and these results highlight the sensitivity of the Antarctic ice coverage to changes in the strength of the winds around the continent."

There has been contrasting climate change observed across the Antarctic in recent decades. The Antarctic Peninsula has warmed as much as anywhere in the Southern Hemisphere, while East Antarctica has shown little change or even a small cooling around the coast. The new research improves understanding of present and future climate change. It is important to distinguish between the Antarctic Ice Sheet — glacial ice — which is losing volume, and Antarctic sea ice — frozen seawater — which is expanding.

The paper Wind-driven trends in Antarctic sea ice motion by Paul R. Holland of British Antarctic Survey and Ron Kwok of the Jet Propulsion Laboratory, California, USA is published in Nature Geoscience.